1. Field of the Invention
This invention relates to a method of and an apparatus for inspecting a transparent or translucent object such as a transparent glass vessel for presence or absence of a defect and a shape, a kind and so forth of such defect.
2. Description of the Prior Art
Various methods of inspecting a body of a bottle are already known, and an exemplary one of such conventional methods is disclosed, for example, in European Patent Application Publication No. 0 344 617. According to the method, a body of a bottle is illuminated with light having a striped pattern, and a transmission image of the body is photoelectrically converted by a two-dimensional photoelectric converting apparatus. Then, the transmission image signal is scanned in a direction oblique to the direction of stripes of the striped pattern, and brightness values at least at three points adjacent the scanning line are compared with each other. Then, a noted point which is a centrally positioned one of the three points is detected as a defect point when the brightness value at the noted point is different by an amount greater than a predetermined value from brightness at the other peripheral points on the opposite sides of the noted point, and then presence or absence of a defect is determined in accordance with the thus detected defect point.
The inspecting method is based in short on the fact that, where the striped pattern is, for example, a pattern wherein white and black stripes or bands repeat alternately, if a bottle has a defect, then either a black transmission image is successively produced in a white stripe or a white transmission image is successively produced in a black stripe, by a light blocking property or a refracting property of such defect, but on the contrary if a bottle has no defect, then no such image is produced or such images are produced but discretely. Where a point A among three points A, B and C which are spaced by a predetermined distance from each other is determined as a noted point, if both of absolute values of differences in brightness between the points A and B and between the points A and C exceed a preset value, then the point A is determined as a defect point.
However, according to the conventional inspecting method, while presence or absence of a light blocking defect such as a foreign article or a soil or a refracting defect such as a foam, a line or a wrinkle, a kind or a shape of such defect cannot be discriminated. Further, where the defect is small in size, even judgment of presence or absence of such defect is difficult by picture image processing. While defects are roughly divided into those which arise from glass itself and those which arise from shaping, if a kind and a shape of a defect can be determined, than a cause of production or a process of production of such defect can be recognized, and consequently, a countermeasure for preventing such defect can be taken readily and promptly. Therefore, it is very important to discriminate a kind and a shape of a defect in order to assure stabilization in quality of products.